I don't have specific numbers on strength and duarability, but I have had both and repaired both rather often. I work with a scout troop that has currently 22 floating canoes.
The protector we put on both is the same, the hole repair method is the same the only real difference is when you dent or completely wrap the Royalite canoe around a rock.
With the Royalex we would get it to the shore and putt the gear out and if it was a small dent just pop it back out usually with a kick and if it were completely wrapped then a little jumping on it might be called for.
When our Royalite canoes dent you can pop it back out but there is a meaner sound to it and the creases where it was bent look much worse. When we wrapped a Royalite canoe around a rock it looked so bad after getting it flat enough to get it off the river that we ended up not using it again.
Bottom line we don't use them in white water any more. We use rafts or Inflatables. If you're not going to be in whitewater then it doesn't matter as much. If you are then the question becomes one of will there be porting? No porting then the weight saving is not that big of a deal.
Update: I went out and checked the canoes, and our maintenance records. The Royalite ones seem to get deeper holes more often and crack at a much younger age. I knew I didn't like them for white water but I think I will steer clear of them after this realization.